Method for continuous quenching of aluminum strip



July 26, 1966 R. M. GRIFFITH METHOD FOR CONTINUOUS QUENCHING OF ALUMINUM STRIP Filed Aug.

I N VEN TOR.

20552?- M. GE/FF/ TH A TTORNEY United States Patent 3,262,822 METHOD FOR CONTINUOUS QUENCHING OF ALUMINUM STRIP Robert M. Griffith, Spokane, WHSIL, assignor to Kaiser Aluminum & Chemical Corporation, Oakland, Calif.,

a corporation of Delaware Filed Aug. 29, 1963, Ser. No. 305,260 3 Claims. (Cl. 14813) This invention relates to quenching continuously heat treated metal strip as it emerges from a continuous heat treating furnace. More particularly, the invention relates to a quenching method which can be incorporated in a continuous heat treating system for treating aluminum alloy strip.

The thermal treatment known as solution heat treating refers to a procedure whereby heat treatable aluminum alloys are heated to an elevated temperature below the melting point and held at that temperature for a sufficient time to allow the constituents of the alloy to go into solid solution. The temperature range to which the particular aluminum alloy should be heated to accomplish satisfactory dissolution of the alloying constituents is referred to as the solution 'heat treating temperature and generally varies with each heat treatable alloy. After heating the alloy to the solution heat treating temperaure and holding to accomplish dissolution, it is then necessary to accomplish a rapid reduction in temperature of the heat treated alloy (i.e., quench) to maintain the alloying constituents in solid solution at room temperature. The reduction in temperature of the heat treated alloy must be accomplished very quickly and, in fact, within a critical time period. For some alloys to develop certain properties, e.g. stress corrosion resistance, it is necessary to achieve a reduction in temperature at a rate of at least about 1000 F. per second. Any commercial continuous heat treating system, in order to be operable on a sufliciently large variety of aluminum alloy stock for all purposes must include a quenching procedure which is capable of continuously quenching metallic strip as it emerges from the heat treating furnace at rates up to about 1000" F. per second or more. The difficulty in achieving this quenching rate is magnified in continuous systems due to the fact that the metallic strip is continuously withdrawn from the heat treating furnace at rates of to 150 feet per minute.

As an illustration of the difficulty encountered in quenching continuously heat treated aluminum alloy strip, in order to satisfactorily solution heat treat aluminum alloy 2024 to increase its stress corrosion resistance level it is necessary to quench this material from the solution heat treating temperature through a temperature range of 7'50-500 F. at a rate in excess of 1000 F. per second. If a strip of this alloy is traveling through a heat treating furnace at 10 feet per minute it is necessary to perform the aforementioned 250 temperature reduction in a distance of about 0.5 of an inch. Moreover, the quenching must occur immediately after the strip emerges from the heat treating furnace in order to preclude any significant premature cooling of the strip prior to quenching. If the quenching is not performed properly the entire solution heat treatment will be wasted and the product will not possess the physical properties required.

In current solution heat treating practice wherein aluminum alloy strip is treated in batch operations, the strip is quenched by immersion in a water bath. Water bath immersion has also been suggested for use in continuous heat treating systems. However, it has been found that such operations are generally inefficient and result in high scrap losses. Difficulty with water bath immersion quenching results from the necessity of immersing the strip without support and in a substantially vertical plane into the bath. (Water bath immersion necessarily is performed with a strip in a vertical or substantially vertical plane.) The unsupported strip frequently develops lengthwise wrinkles (roping) due to the severe contraction of the strip upon cooling when the heat treated strip is dropped in a container of water. If roping occurs the strip cannot be rolled effectively because the lengthwise wrinkles become ironed into the strip upon passage over rolls. It has been determined that in order to satisfactorily quench continuously heat treated aluminum strip, the strip must remain in a substantially horizontal position so that lengthwise wrinkles which may form during quenching will be avoided and the strip will be in a satisfactory condition for subsequent processing.

Aluminum strip at the elevated temperatures required for solution heat treating is extremely soft and easily marred and scratched. In continuous heat treating systems where the strip is treated in a substantially horizontal plane the difliculty of supporting the strip, which is exceptionally soft at the elevated temperature, becomes a very serious problem. With the advent of recent supporting techniques employing gaseous supporting mediums, the problem of supporting the strip during traverse of the heat treating furnace has been largely avoided. However, the support of the strip during quenching has continued to present a difficult problem.

The present invention provides a method of quenching continuously heat treated aluminum strip as it emerges from a continuous heat treating furnace which avoids all of the above-mentioned diiiiculties and which enables the efiicient and continuous production of heat treated aluminum alloy strip of satisfactory properties. According to the invention, a quenching method is provided which can be included in a continuous heat treating system which comprises withdrawing heat treated aluminum strip in a substantially horizontal position from a heat treating furnace and contacting the strip in the substantially horizontal position with at least one water spray to quench the strip. The spray or sprays impinge against the strip at a predetermined impingement angle less than and with a sufficient velocity to substantially avoid the formation of a steam film on the strip. The strip is supported in a substantially horizontal position with the water spray or sprays during quenching. Thus, according to the invention the heated aluminum alloy strip does not contact any supporting structure which might mar or damage the strip in any way during quenching. The use of at least one water spray to both quench the strip and support the strip in a horizontal position enables solution heat treated aluminum alloy strip to be quenched in a continuous system in a manner to produce a high quality product of a variety of alloy compositions.

The invention can be better understood by referring to the accompanying drawing which is a side elevation of a quenching assembly useful for quenching according to the invention.

As can be seen, aluminum strip 10 is continuously with drawn from a heat treating furnace 12 and passed through quenching chamber 20 within a quenching assembly enclosure 18. Metallic strip 10 is in a substantially horizontal position as it is withdrawn from heat treating furnace 12. Upon entering quenching chamber 20 aluminum strip 10 is contacted with water sprays from nozzles 22a and 22b constituting the primary spray means. In the preferred embodiment quench water is sprayed only on the bottom of the strip and nozzles are used in the primary spray means which provide a fan of water having a spray pattern of uniform density and a fan width at the pass line in excess of the maximum strip Width. One or more nozzles may be employed in this way to provide a spray pattern of uniform density extending over the width of the entire strip. In the drawing nozzle 22a is shown projecting a spray at a 65 angle and nozzle 22b is shown in position to project a spray at 80 in such a way as to complement the spray from nozzle 22a. It is important to provide a spray from the primary spray means of uniform density in order to obtain a uniform quench rate. Uniformity in quenching is an important factor in the pro duction of flat metal strip with minimum distortion and lengthwise wrinkles. It has been found that two nozzles 22a and 22b positioned as shown are capable of quenching a large variety of strip widths. The quenching nozzles of the primary spray means should also be positioned as close to the furnace as possible to avoid any significant premature cooling prior to the major temperature reduction. The nozzles employed should be of a type which will provide a sufficient volume of spray at a necessary velocity to be capable of accomplishing a temperature reduction of up to about 2000 F. per second throughout the critical temperature ranges of the various alloys. Subsequent rows of nozzles 24 and 26, constituting secondary spray means, are disposed downstream of the primary spray means to support and further cool the strip to a temperature for safe handling. The nozzles are positioned in such a way to support the untensioned strip and hold it away from structural components which might otherwise mar or scratch the metal. Means 14, 15 and 16 are provided to supply water under controlled pressure to the sprays of the primary and secondary spray means. Squeegee rolls 32 and air drying unit 38, equipped for valved air knife assemblies 34 and 36, are located outside the quenching chamber and serve to remove remaining water from the strip so that the strip can be processed further, e.g., rolled, cut, etc.

The angle of impingement of the water spray upon the strip is adjustable from 90-45 from the horizontal. Although optimum quench rates are obtained with a 90 impingement angle, projecting a spray at such an angle results in considerable splashback of water into the furnace. Angles of impingement of less than 45 do not provide acceptable quench rates on heavier gauges. Moreover, a decreasing impingement angle also lengthens the distance between the furnace and the quench line within which the water spray can contact the strip. If the strip is allowed to proceed too far before quenching, premature cooling may occur which would preclude obtaining maximum properties. It has been determined that an impingement angle of from about 85 55 enables adequate quench rates with minimum splashback of water into the furnace and premature cooling, and an angle of 60-70 is preferred. Impingement angle of the spray referred to above is the angle generated counterclockwise from a horizontal reference plane.

The volume of spray water required to cool the strip has been found to be proportional to the strip thickness when fan sprays of predetermined fan widths are employed. Water pressure must also be adjusted to enable the spray to support the untensioned strip as it moves through the quenching chamber. Water pressure can be adjusted by any suitable means including adjustable throttling valves provided on each spray header. Pressure gauges can be installed at suitable locations as, for example, on each header between the nozzle and the valve to indicate the various water pressures. Spray velocities resulting from header pressures of from about 20-60 p.s.i. have been found to be satisfactory for a wide variety of aluminum strip compositions and gauges.

It is apparent from the above that various changes and modifications may be made without departing from the invention. For example, water spray can be directed against the strip from both beneath and above the strip if care is exercised to avoid splashback into the heat treating furnace. A protective air curtain or other suitable barrier may be employed. Similarly, the fluid used for quenching, i.e., extracting heat from the strip to lower its temperature, obviously could be other substances than water. Moreover, if water is used, additives or other materials could be used in combination therewith. However, the properties of the sprays, e.g. volume, velocity, density, etc., must be adjusted so that the strip is entirely supported by the spray during quenching and a substantially uniform quench rate is achieved throughout a cross section of strip. In addition, as discussed above, major temperature reduction through critical temperature ranges must be accomplished before significant premature cooling of the strip from solution heat treating temperature occurs.

Accordingly, the scope of the invention should be limited only by the appended claims, wherein what is claimed is:

-1. A method of quenching continuously heat treated aluminum strip as it emerges from a continuous heat treating furnace comprising withdrawing heat treated aluminum strip in a substantially horizontal position from said furnace, contacting said strip in said substantially horizontal position with at least one water spray to quench said strip, said spray impinging against said strip at a predetermined impingement angle less than 90 and with a sufiicient velocity to avoid the formation of a substantial steam film on said strip, and supporting said strip in said substantially horizontal position with said water spray during quenching.

2. A method according to claim 1 wherein said spray impinges on said strip at an angle of about -55 from the horizontal.

3. A method according to claim 1 wherein said aluminum strip is supported during quenching with a plurality of water sprays directed against the undersurface thereof.

References Cited by the Examiner UNITED STATES PATENTS 2,175,599 10/1939 Finkbone et a1 2666 2,776,230 1/1957 Scott l48153 2,878,621 3/1959 Zellers et al. 26697 X 3,03 6,825 5/1962 Eisenmenger 2664 JOHN F. CAMPBELL, Primary Examiner. JAMES H. TAYMAN, Examiner.

J. I. MULLEN, M. L. FAIGUS, Assistant Examiners. 

1. A METHOD OF QUENCHING CONTINUOUSLY HEAT TREATED ALUMINUM STRIP AS IT EMERGES FFROM A CONTINUOUS HEAT TREATING FURNACE COMPRISING WITHDRAWING HEAT TREATED ALUMINUM STRIP IN A SUBSTANTIALLY HORIZONTAL POSITION FROM SAID FURNACE, CONTACTING SAID STRIP IN SAID SUBSTANTIALLY HORIZONTAL POSITION WITH AT LEAST ONE WATER SPRAY TO QUENCH SAID STRIP, SAID SPRAY IMPINGING AGAINST SAID STRIP AT A PREDETERMINED IMPINGEMENT ANGLE LESS THAN 90* AND WITH A SUFFICIENT VELOCITY TO AVOID THE FORMATIION OF A SUBSTANTIAL STEAM FILM ON SAID STRIP, AND SUPPORTING SAID STRIP IN SAID SUBSTANTIALLY HORIZONTAL POSITION WITH SAID WATER SPRAY DURING QUENCHING. 